Interfaces for a photoionization mass spectrometer

ABSTRACT

A detector system that contains two inlet port coupled to a photoionization chamber. One inlet port allows for the introduction of a test sample. The test sample may contain contaminants, drugs, explosive, etc. that are to be detected. The other port allows for the simultaneous introduction of a standard sample. The standard sample can be used to calibrate and/or diagnose the detector system. Simultaneous introduction of the standard sample provides for real time calibration/diagnostics of the detector during detection of trace molecules in the test sample. The photoizonizer ionizes the samples which are then directed into a mass detector for detection of trace molecules. The detector system may also include inlet embodiments that allow for vaporization of liquid samples introduced to a low pressure photoionizer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.596,307, filed on Jun. 14, 2000, pending, which is acontinuation-in-part of application Ser. No. 247,646, filed on Feb. 9,1999, U.S. Pat. No. 6,211,516.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject matter disclosed generally relates to.a detector that candetect trace molecules.

2. Background Information

There are detectors that are capable of detecting a trace molecule froma sample. The sample may be a gas or liquid sample taken from a room ora fluid source, respectively. It may be desirable to detect certaintrace molecules to determine whether the sample contains contaminants,drugs, explosives, etc.

The detector may include an ionization stage and a mass detector stage.The ionization stage ionizes molecules within the sample and thenprojects the ionized molecules through the mass detector. The massdetector may be a time of flight device that determines mass based onthe time at which the molecules strike a detector plate. The ionizationchamber may include a light source that ionizes the sample through aphotoionization process.

The sample is introduced into the ionization chamber through a singleinlet port. To obtain accurate readings it is desirable to calibrate thedetector before each sample is run through the device. The detector iscalibrated by introducing a standard sample that may contain themolecules under investigation. obtaining accurate readings thereforerequires sequentially loading a standard sample, calibrating thedetector and then introducing a test sample into the ionization chamber.This sequence can be time consuming particularly when large batches ofsamples are to be tested. Additionally, there may be some degradation inthe detector between the time the detector is calibrated and when thetest sample is actually loaded into the chamber. It would be desirableto decrease the run time and increase the accuracy of a detector.

Liquid test samples typically include water or drug samples stored inorganic solvents. It is desirable to vaporize the solvent before thesample is ionized. One way to vaporize the solvent is to break thesample into aerosol droplets with a nebulizer. A nebulizer includes aco-flow of inert gas that breaks the liquid sample into an aerosol. Thedetector may contain a heating element that vaporizes the solvent withinthe aerosol.

Most nebulizers operate at atmospheric pressure because higher pressurecauses more molecular collisions and assist in the vaporization process.It is sometimes desirable to operate the ionization chamber at lowpressure, particularly for photoionizers. It would be desirable toprovide an inlet port for liquid samples that can introduce the sampleto a low pressure ionization chamber.

BRIEF SUMMARY OF THE INVENTION

A detector system that includes a detector coupled to a photoionizer.The system may also include a first inlet port and a second inlet portthat are both coupled to the photoionizer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a detector system;

FIGS. 2A-B are graphs showing the detection of a standard sampleintroduced to the detector;

FIGS. 3A-B are graphs showing the detection of a test sample andstandard sample simultaneously introduced to the detector;

FIG. 4 is an illustration of an alternate embodiment of the detector;

FIG. 5 is an illustration of an alternate embodiment of the detector;

FIG. 6 is an illustration of an alternate embodiment of the detector;

FIG. 7 is an illustration of a syringe used to introduce a test sampleinto the detector;

FIG. 8 is an illustration of a nebulizing inlet port that receives asyringe;

FIG. 9 is an illustration of a nebulizing inlet port that receives acapillary tube.

DETAILED DESCRIPTION

Disclosed is a detector system that contains two inlet ports coupled toa photoionization chamber. One inlet port allows for the introduction ofa test sample. The test sample may contain contaminants, drugs,explosive, etc. that are to be detected. The other port allows for thesimultaneous introduction of a standard sample. The standard sample canbe used to calibrate and/or diagnose the detector system. Simultaneousintroduction of the standard sample provides for real timecalibration/diagnostics of the detector during detection of tracemolecules in the test sample. The photoionizer ionizes the samples thatare then directed into a mass detector for detection of trace molecules.The detector system may also include inlet embodiments that allow forvaporization of liquid samples introduced to a low pressurephotoionizer.

Referring to the drawings more particularly by reference numbers, FIG. 1shows a detector system 10. The detector system 10 may include a housing12, electrostatic lenses 14 and 16, sealing elements 18 and an ionizer20 that surround an ionization chamber 22. In one embodiment the ionizer20 is a light source that can photoionize molecules within the chamber22. By way of example, the light source can emit light havingphoto-energy between 8.0 and 12.0 electron volts (eV). 8.0 to 12.0 eV ishigh enough to ionize most trace molecules while minimizing molecularfragmentation within the sample.

The detector system 10 may include a first inlet port 24 and a secondinlet port 26 that are coupled to the ionization chamber 22. The inletport 24 allows a test sample to be introduced to the ionization chamber22. The test sample may contain contaminants, drugs, explosives, etc.that are to be detected by the detector system 10. The second inlet port26 allows for the introduction of a standard sample that can be used tocalibrate and/or diagnose the detector system 10. The standard samplemay be introduced in a continuous manner so that there is a consistentflow of the sample. The test sample is typically introduced through asyringe. Consequently, the introduction of the test sample is atransient event. Both the test sample and the standard sample may beeither a liquid or gas flow.

The first inlet port 24 may include a septum 28 and a septum cap 30. Theseptum 28 can receive the needle of a syringe (not shown). The firstinlet port 24 may be coupled to the ionization chamber 22 by a channel32. The housing 12 may include a heating element 34 embedded in thehousing 12 to heat the channel 32. The heating element 34 may operate ata temperature that vaporizes solvents in the test sample. For example,the heating element 34 may operate between 100 and 400 degreescentigrade.

The second inlet port 26 may include a capillary tube 36 that extendsthrough a tube fitting 38. The housing 12 includes another channel 40that provides fluid communication between the tube 36 and the ionizationchamber 22. The heating element 34 also extends to the channel 40 tovaporize the sample introduced through the capillary tube 36. Althoughthe first inlet port 24 is shown as having a septum, it is to beunderstood that the first port 24 may have the capillary tubearrangement of the second port 26.

The ionizer 20 ionizes the samples introduced to the ionization chamber22. The lenses 14 and 16 then pull the ionized molecules of the samplesthrough an aperture 42 and into a mass detector 44. The mass detector 44may be a time of flight device that can detect the trace molecules basedon the time required to strike a detector plate (not shown) within thedetector 44. Although a time of flight mass detector is described, it isto be understood that other types of detector devices may be used in thesystem 10.

FIGS. 2A and 2B show a mass spectrum and a time dependent profile,respectively, for a standard sample introduced to the detector. Thestandard sample can be used to calibrate and/or diagnose the detectorsystem.

FIGS. 3A and 3B show a mass spectrum and a time dependent profile,respectively, for a combined standard sample and a test sample thatcontains diazepam in methanol, introduced to the detector system 10. Asshown in FIG. 3B, the sample signal rises and falls with theintroduction of the test sample.

FIG. 4 shows an alternate embodiment, wherein the detector 10′ includesa pump 46 that removes a portion of the samples. It is desirable tocontrol the flow of the samples from the ionization chamber 22 to themass detector 44. An excessive flow may create an undesirably highpressure within the mass detector 44. A pump-out channel 48 may beconnected to a point between the ionization chamber 22 and the aperture42 to divert some of the ionized molecules away from the mass detector44. FIG. 5 shows an embodiment of a detector 10″ wherein the channel 48terminates in the ionization chamber 22′.

FIG. 6 shows another embodiment of a detector system 200 that includes afirst ionization chamber 202 coupled to a second ionization chamber 204by a capillary tube 206. The chambers 202 and 204 may be separated byinterface walls 208.

The first ionization chamber 202 may include a first ionizer 210. Thefirst ionizer 210 may be of any type to ionize molecules within thefirst chamber 202. The ionized molecules within the first chamber 202are focused into the capillary tube 206 by electrostatic lenses 212 and214. The first ionization chamber 202 operates at a higher pressure thanthe second chamber 204. The pressure differential drives the ionizedmolecules from the first chamber 202, through the tube 206 and into thesecond chamber 204.

By way of example, the first chamber 202 may operate at atmosphericpressure. Such a high pressure may induce molecular collisions andreactions that can change the identity of the ions. The secondionization chamber 204 may contain a second ionizer 216 that furtherionizes the sample. Further ionization may generate the original ionsand therefore restore the identity of the ions. The second ionizer 216may be a photoionizer. A photoionizer may ionize molecules not ionizedby the first ionizer 208 and thus provide more information.Additionally, a photoionizer is desirable because it does not useelectric fields and therefore such a device will not interfere withionized molecules traveling through the aperture 218 of the focusinglens 220 to the mass detector 222.

A second capillary tube 224 can be placed adjacent to the first tube206. The second capillary tube 224 may provide a standard sample that isnot ionized within the first ionization chamber 202. The standard sampleflows into the second chamber 204 due to the differential chamberpressure. The standard and test samples are ultimately detected withinthe mass detector 222,

FIG. 7 discloses a syringe 300 that can be used to introduce a testsample into the detector system. The syringe 300 may include a needle302 that is attached to a tube 304. The tube 304 has an inner chamber306. A plunger 308 extends into the inner chamber 306 of the tube 304.

The syringe 300 may be loaded with a liquid test sample 310 that isupstream from a volume of air 312. The air mixes with and dilutes theliquid test sample to increase the delivery time of the test sample intothe detector system. It is desirable to increase the delivery time toimprove the vaporization of the solvent in the sample. The mixing of theair and liquid sample also allows for a larger syringe needle 302 thatis less susceptible to clogging and condensation. The air volume mayalso nebulize the liquid into an aerosol. An aerosol state is preferredto induce vaporization of the solvent within the liquid sample.

A low pressure source can draw out the sample in a syringe without usingthe plunger. It is sometimes desirable to control the rate of sampledelivery. The combination of air and liquid reduces the total mass flowrate into the detector system, which reduces the pressure surge that canresult from injection of a pure liquid sample. The volume flow rate of agas is typically about 30 times greater than for a liquid. However,because the density of gas is about 1/600 of the density of the liquid,the mass flow rate of the gas is about 20 times less than for theliquid. It is desirable to have a significantly high air to liquid ratio(much more air than liquid), but the ratio of gas to liquid should be noless than 1:1.

The syringe may contain a solvent slug 314 that washes out any residualsample within the needle 302. It has been found that analyte maycondense within the needle 302 of the syringe 300. The solvent slug 314will wash through any such condensation. The solvent slug 314 mayinclude the standard sample used to calibrate and/or diagnose thedetector system. By way of example, the syringe 300 may contain 5microliters of air 312, 1 microliter of sample liquid 310 and 1microliter of solvent slug 314.

FIG. 8 shows an embodiment of an inlet port 400 with an integratednebulizer. The inlet port 400 is coupled to an ionization chamber (notshown). The inlet port 400 includes a septum 402 that receives a needle404 of a syringe 406. The syringe 406 can inject a sample into an innerchannel 408 of a housing 410. The housing 410 may include a heatingelement 412.

The inlet port 400 may further have a co-flow port 414 that introduces agas into the inner channel 408. The gas introduced through the co-flowport 414 breaks the liquid into an aerosol. The aerosol facilitates thevaporization of solvents and analyte molecules on the heating element412. The inlet port 400 may further includes a restrictor 416 thatinduces a vigorous mixing of the air and liquid sample into aerosoldroplets. The aerosol droplets are pulled through the restrictor 416 bythe pressure differential between the channel 408 and the ionizationchamber (not shown) of the detector system.

FIG. 9 shows an alternate embodiment of an inlet port 400′ that utilizesa capillary tube 418 and tube interface 420 instead of the syringe 406and septum 402 shown in FIG. 8.

The generation of aerosol droplets and vaporization can be augmented bya vibrator 422. The vibrator 422 may contain piezoelectric elements orother means for shaking either the syringe 406 or capillary tube 418.The vibration may break the liquid stream into small aerosol droplets.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

1. A detector system, comprising: an ionization chamber; a first ionizercoupled to said ionization chamber; a first inlet port coupled to saidphotoionizer; an intermediate chamber coupled to said ionizationchamber; a second ionizer coupled to said intermediate chamber; a pumpcoupled to said intermediate chamber; and, a detector coupled to saidionization chamber.
 2. The system of claim 1, wherein said first inletport includes a syringe port.
 3. The system of claim 1, wherein saidsecond inlet port includes a capillary tube.
 4. The system of claim 1,wherein said first inlet port includes a capillary tube.
 5. The systemof claim 1, wherein said first inlet port includes a nebulizer.
 6. Thesystem of claim 1, further comprising a pump coupled to saidphotoionizer.
 7. The system of claim 1, wherein said first inlet portincludes a heating element.
 8. The system of claim 1, wherein saidsecond inlet port includes a heating element.
 9. The system of claim 1,further comprising a syringe that is coupled to said first inlet port,said syringe containing a volume of air upstream from a sample.
 10. Thesystem of claim 9, wherein said syringe includes a solvent slug locateddownstream from the sample.
 11. A detector system, comprising: anionization chamber; a first ionizer coupled to said ionization chamber;port means for introducing a test sample to said ionization chamber; anintermediate chamber coupled to said ionization chamber; a secondionizer coupled to said intermediate chamber; a detector coupled to saidintermediate chamber; and, pump means for pumping a portion of thesample from said intermediate chamber.
 12. The system of claim 11,wherein said first port means includes a syringe port.
 13. The system ofclaim 11, wherein said second port means includes a capillary tube. 14.The system of claim 11, wherein said first port means includes acapillary tube.
 15. The system of claim 11, wherein said first portmeans includes a nebulizer.
 16. The system of claim 11, furthercomprising pump means for diverting a portion of the test and standardsamples away from said detector.
 17. The system of claim 11, whereinsaid sport means includes a heating element.
 18. The system of claim 11,wherein said second port means includes a heating element.
 19. Thesystem of claim 11, wherein said sport means includes a syringe thatcontains a volume of air upstream from a sample.
 20. The system of claim19, wherein said syringe includes a solvent slug located downstream fromthe sample.
 21. A method for detecting a trace molecule in a sample,comprising: introducing a test sample to a photoionization chamberthrough a inlet port; photoionizing the sample; moving the sample to anintermediate chamber; ionizing the sample in the intermediate chamber;pumping a portion of the sample from the intermediate chamber; moving aportion of the sample into a detector chamber; and detecting the tracemolecule.
 22. The method of claim 21, wherein the sample is nebulized.23. The method of claim 21, wherein the sample is heated.
 24. The methodof claim 21, wherein a portion of the test and standard samples arediverted away from a detector that detects the trace molecule. 25-48.(canceled)